Refrigerating apparatus



C. H. WURTZ Jan. 24, 1956 REFRIGERATING APPARATUS, INCLUDING DEFROSTING MEANS Filed Jan. 4, 1952 REFRIGERATKNG APPARATUS, INCLUDING DEFROSTEIG MEANS liiford H. Win-t2, Oakwood, Ghio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware Application January 4, 1952, Serial No. 264,915

4 Claims. (Cl. 62-4) This invention relates to refrigerating apparatus and more particularly to a system for defrosting evaporators.

Various systems have been devised for defrosting evaporators automatically but there has always been considerable difficulty in properly locating the thermostat control to obtain the desired control during the operating period and also during the idle period to obtain com lete defrosting. The best location of the thermostat bulb for refrigerant flow control was not the best location for the control of the defrosting operation.

it is an object of my invention to provide a simple thermostatic control system whereby the refrigerant flow may be controlled by the temperature at the location best suited for it, while defrosting is controlled by the temperature at the location best suited for the control of defrosting.

it is another object of my invention to provide a simple control system wherein the switch opening is controlled by one portion of thermostatic bulb system and the switch closing is controlled by another portion of the thermostatic bulb system.

it is another object of my invention to provide a simple control system wherein the quick temperature change caused by the arrival of liquid refrigerant at a certain location is used to control the switch opening while the slow melting of the greatest accumulation of frost is used to delay the switch closing until the defrosting is completed.

To attain these objects I have provided the refrigerating system with a simple snap-acting thermostatic control switch having a capillary tube type of thermostatic bulb system in which one portion of the bulb is clamped directly in intimate thermal heat exchange relation with the portion of the evaporator best suited for controlling the refrigerant flow while the other portion of the capillary tube bulb system is clamped in poor heat exchange relation with the evaporator at a location below the area of greatest frost accumulation so that it will be contacted by the defrost water.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein preferred form of the present invention is clearly shown.

in the drawings:

Fig. l is a vertical sectional view of a two-compartment household refrigerator embodying one form of my invention;

Fig. 2 is a fragmentary sectional view taken along the line 2-2 of Fig. l; and

Fig. 3 is a ragmentary sectional view taken along the line 3-3 of Fig. 1.

Referring non. to Fig. 1, there is provided an outer hermetically sealed sheet metal shell 26 enclosing the cabinet. The joints of this shell are sealed. Within the upper portion of the shell there is provided a freezing compartment 32 in the form of a box-shaped metal States Patent 6 container having its front side open. Beneath the freezing compartment container 32 there is provided a food compartment 38 likewise in the form of a box-shaped metal inner container or liner also having its front side open. The front edges of the box-shaped containers 32 and 33 are connected by breaker strips of heat insulating material with the front wall of the outer shell 20 as is customary in the art. The open front sides of the freezing compartment container 32 and the food compartment container 38 are preferably closed by separate front doors (not shown). The spaces between these containers 32 and 38 and the walls of the outer shell are filled with insulation such as mineral or glass wool enclosed in sealed bags of some suitable material, such as polyethylene.

The freezing compartment container is provided with smooth surfaced inner walls so that any snow or frost accumulating thereon may be readily scraped or brushed off. The freezing compartment container is cooled by the first evaporating stage of a primary refrigerating system which includes a sealed motor compressor unit 55f) which delivers compressed refrigerant to a condenser 52, both of which are located in a machine compartment loll beneath the partition wall 24 of the cabinet 20. The motor compressor unit 50 is preferably of the high side type shown in the Rataiczak Patent 2,377,965 issued June 12, 1945.

The condenser 52 delivers liquid refrigerant through a capillary tube restrictor 54 to the inlet connection 56 of a tubular freezing evaporator which includes a section of serpentine tubing 57 applied to the rear wall of the container 52 and loops 5%, 59 and 60 applied to the ice tray shelves at one side of the container 32. From the loop on the refrigerant passes into the section 61 of evaporator tubing which extends in the heat exchange relation with the top, bottom and sides of the container 32.

After passing through a liquid trap at the end of the tubing 61, the refrigerant is conducted through a supply conduit 72 to a vertical rectangular refrigerated plate type of evaporator @li spaced from, but fastened to, the rear wall of the food compartment container 38 within and near the top of the food compartment. The re frigerated plate fill has a minimum of mass and low hold-over capacity. it is provided with a refrigerant passage 91 which extends along the edges of the refrigerated plate evaporator 99 having its inlet 89 connccted to the supply conduit 72 and its outlet 87 connected to the return conduit 94 adjacent the upper lefthand corner of the plate as shown in Fig. 1. The return conduit M- connects to an accumulator tank 96 located along the upper rear edge of the freezing compartment container 32. The suction conduit extends from this accumulator tank 6 to the suction inlet of the motor compressor unit 50.

The operation of the motor compressor unit St) is controlled by a snap-acting thermostat switch 80, connected in series with the supply conductors 81 of the motor compressor unit Ell. This switch 80 is set to operate upon a defrosting cycle. Its thermo-sensitive element is in the form of a capillary tube 370 which is connected at one end to the operating bellows of the switch 8%. The capillary tube 370 is sealed at its opposite end and is provided with a charge of vapor of some suitable gas such as one of the many refrigerants available today. it is desired to control this refrigerator in such a way that the freezing compartment 32 is maintained in the neighborhood of 0 degrees Fahrenheit at all times and the food compartment is maintained in the neighborhood of about 38 degrees Fahrenheit at all times. It is also desired that frost be. prevented from accumulating on the evaporator 90.

It was discoveredthat it was necessary to connect to the upper left-hand corner of evaporator 90 a secondary Condenser 137 in the form of a long vertical tubular member as shown with its extreme upper portion clamped by the clamp 93 in heat exchange relation with the adjacent portions of the supply and return conduits 72 and 94 and its lower portion in heat exchange relation with the portion of the evaporator 90 beneath the connections of the conduits 72 and 94 for the purpose of preventing the accumulation of frost, particularly upon the adjacent portions of the tubing 72 and $4. This secondary condenser 137 connects to a secondary evaporating portion 131 surrounding the lower portion of the food compartment liner 38 for providing additional cooling for the two ventilated vegetable drawers 127 and 129 provided in the bottom of the food compartment 33. The secondary evaporator 131 absorbs sufficient heat and transmits the heat through the secondary refrigerant circult to the vertical tubular condenser 137 to prevent the accumulation of frost from cycle to cycle upon the connections 72 and 94 and the left-hand side of the refrigerated plate evaporator 90.

As a result of this, the defrosting is hastened in the left portion of the plate 90 and the right side of the refrigerating plate 90 becomes the last to defrost. Consequently it is desired to control the closing of the switch by the temperature of the plate 90 nearest the right edge of the plate 90. However it was found that if the opening of the switch also was controlled by the temperature of this portion of the plate 94 that only one half of the plate 90 was being effectively used for cooling the food compartment 38 and as a result the food compartment liner 38 was not kept at a low enough temperature under warm room temperatures. For controlling the opening of the switch 80 it is desirable that this be done in accordance with the temperatures adjacent the left side of the plate 90, at the section .lines 33.

By my particular system, I am able to control the opening of the switch 80 by the temperature adjacent the plate 90 where the section lines 33 are located while closing of the switch 80 is controlled by the temperature of the plate 90 adjacent the section lines 22. The control of the opening of the switch is accomplished by providing a temperature sensitive serpentine portion 371 at the extreme end portion of the capillary tube thermostatic element 370 and clamping it directly to the back of the plate 90 in intimate heat exchange relation by clamping member 372. The control of the closing of the switch is provided by a temperature sensitive serpentine section 373 provided in the temperature sensitive capillary tube element 370 which is clamped to the rear face of the plate 90 adjacent its lower right-hand edge by a clamp 374.

However to prevent this serpentine section 373 from controlling the Opening of the switch 80, I provide an insulating spacer 375 between the serpentine portion 373 and the adjacent rear face of the plate 90 as shown in Fig. 2. This insulating spacer 375 delays the heat transfer when liquid refrigerant passes through the adjacent portion of the passage 91 so that the switch 86 is not caused to open upon this occurance, but this opening is delayed until the liquid refrigerant reaches a portion of the passage 91 adjacent the serpentine section 371. This insulating spacer may be made of a suitable thermoplastic material such as phenolformaldehyde resin.

As a result of this, the switch 80, which is normally set to open at about degrees Fehrenheit, will not open under warm room temperatures and warm food compartment temperatures until liquid refrigerant at or below the temperature at which the switch 36 is set to open reaches approximately the location of the serpentine portion 371. Because of the nearness of the vertical tubular condenser 137, the left-hand portion of the plate 99 will always be at a higher temperature than the right-hand portion of the plate 90 so that the temperature of the serpentine portion 371 will not control the closing of the switch 80. This is because of the characteristics of the vapor charge in the capillary tubing 370 which causes the pressure within the tubing 370 and the actuating bellows of the switch to be in accordance with the temperature at the lowest point in the system. Therefore since the right side of the plate in colder than the left side during the idle period of the refrigerating system and since the temperature change is very slow during this idle period, the serpentine portion 373 will always be at a lower temperature than the serpentine portion 371 during the idle period of the refrigerating system. There is sufficiently rapid heat flow through the insulating spacer 375 during the idle period that the temperature of the serpentine portion 373 is substantially the same as the adjacent portion of the plate 98 to which it is clamped. The serpentine portion 373 is so located that the water from any melting frost on the right side of the plate 90 will contact the serpentine portion 373 and kept it substantially at the temperature of the frost so that the closing of the switch 80 will be prevented until the complete melting of the frost stops the flow of the defrost water over the surfaces of the serpentine portion 373.

In this way, a more favorable control system is obtained which insures the maintenance of desired temperatures in both the freezing and food compartments 32 and 38, as well as the complete defrosting of the plate 90 at the end of each idle period. The defrost water may be collected in a pan 162 in the machine compartment 161 where it is evaporated by the circulation of warm air.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. Refrigerating apparatus including an above freezing food compartment and a below freezing compartment, a thermal heat transfer barrier between said compartments, a refrigerant liquefying means, a freezing evaporating means in heat exchange relation with said below freezing compartment and having its inlet connected to an outlet of said liquefying means, a food compartment evaporating means in heat exchange relation with said food compartment and having its inlet connected to an outlet of said freezing evaporating means, means for returning evaporated refrigerant from said freezing and food compartment evaporating means to said liquefying means, and thermostatic cycling control means set to operate upon a defrosting cycle for controlling the operation of said liquefying means, said food compartment evaporating means including a refrigerant passage extending from its inlet to its outlet, said control means including a first thermosensitive element located in intimate heat exchange relationship with one portion of the food compartment evaporating means, said control means also including a second thermosensitive element located in poor heat exchange relationship with another portion of the food compartment evaporating means.

2. Refrigerating apparatus including an above freezing food compartment and a below freezing compartment, a thermal heat transfer barrier between said compartments, a refrigerating liquefying means, a freezing evaporating means in heat exchange relation with said below freezing compartment and having its inlet connected to an outlet of said liquefying means, a food compartment evaporating means in heat exchange reiation with said food compartment and having its inlet connected to an outlet of said freezing evaporating means, means for returning evaporated refrigerant from said freezing and food compartment evaporating means to said liquefying means, and thermostatic cycling control means set to operate upon a defrosting cycle for controlling the operation of said liquefying means, said food compartment evaporating means including a refrigerant passage extending from its inlet to its outlet, said control means including a first thermosensitive element located in intimate heat exchange relationship with one portion of the food compartment evaporating means, said control means also including a second thermosensitive element located in poor heat exchange relationship with another portion of the food compartment evaporating means, said food compartment evaporating means in the part near the first thermosensitive element being provided with a. secondary refrigerant condenser.

3. Refrigerating apparatus including a refrigerant evaporator having a refrigerant passage provided with an inlet and an outlet, refrigerant liquefying means, means for supplying liquid refrigerant to said evaporator from said refrigerant liquefying means, a thermostatic cycling control means set to operate upon a defrosting cycle for controlling the operation of said liquefying means, said control means including a first thermosensitive element located in intimate heat exchange relationship with one portion of the evaporator, said control means also including a second thermosensitive element attached to but located in poor heat exchange relationship with another portion of the evaporator in the path of defrost water draining from said evaporator, and means to apply localized heat to one of said evaporator portions.

4. Refrigerating apparatus including an upright rectangular plate type evaporator having a refrigerant passage cxtending along the edges thereof with the inlet and outlet located adjacent an upper corner thereof, supply and suction conduits connecting to said inlet and outlet, refrigerant liquefying means, means for supplying liquid refrigerant to said evaporator from said refrigerant liquefying means, and thermostatic cycling control means set to operate upon a defrosting cycle for controlling the operation of said liquefying means, said control means including a first thermosensitive element located in intimate heat exchange relationship with one portion of the evaporator, said control means also including a second thermosensitive element spaced from said first element and located in poor heat exchange relationship with the lower edge portion of the evaporator in the path of defrost water draining from said evaporator.

References Cited in the file of this patent UNITED STATES PATENTS 

